The following text should not be construed as an admission of knowledge in the prior art. Furthermore, citation or identification of any document in this application is not an admission that such document is available as prior art to the present disclosure, or that any reference forms a part of the common knowledge in the art.
A fundamental challenge in the field of prosthetic device development is to find a design that balances functionality with cost. The amputee desires a prosthetic device that both mimics and feels like the natural component that has been lost, for example, a finger or a hand. The replacement device must also be affordable. This need for cost effective prosthetic appliances is especially prevalent in poor countries and those suffering from civil war or natural disasters, such as Haiti or several African nations such as Sierra Leone, Uganda, and Kenya.
The human hand is an amazingly complicated feat of engineering, and very difficult to emulate. Even individual human fingers have an incredible range of motion and dexterity. This is especially evident when watching the fine motor skills of a sculptor, guitarist or surgeon. These motions are very difficult to mimic with an artificial device, especially in a cost-effective manner. In general, the engineering designs that most successfully mimic nature are also the most expensive. These designs can be described as “bionic”, usually costing thousands of dollars to manufacture and maintain, or they are destined to remain relegated to the laboratory or to be used only by the most wealthy. The vast majority of people in need of affordable prosthetic devices lack the means to acquire these technologically sophisticated designs. Wonderful engineering feats in themselves, most bionic designs are not economically viable solutions for the masses. However, the other extreme is also lacking. More affordable prosthetic appliance designs tend to have short life spans, high failure rates, and are often expensive or difficult to maintain. From the amputee's perspective, these cheaper designs also tend to provide much less functionality and utility. It is one objective of the present disclosure to provide a prosthetic design that offers a balance of affordability and functionality.
A fundamental element of any prosthetic device that provides motion, for example an artificial arm, hand or finger, is a joint. Without one or more joints, a finger is simply a lever with severely limited functionality. Joints provide the means needed to flex or extend the digit, allowing for control to pick-up and grasp objects, ranging from such things as a hammer to a delicate wine glass.
Despite their importance, viable prosthetic joint designs are surprisingly limited, the vast majority relying on a pin that rigidly restricts motion to revolution about a single axis. Although simple in concept, “pin joints” do not mimic their natural counterparts, which are held together by a number of flexible ligaments. Knees, elbows, wrists, and fingers all rely upon ligaments for motion, typically biased to one plane but having some ability to move in all three spatial dimensions, including some rotational motion around an axis. Pins, on the other hand, limit motion to pure rotation, thus giving prosthetic appliances an artificial, rigid, and almost robotic motion.
Nevertheless, history has shown a propensity and preference for the pin (or screw, nail, rod, peg, or pinion). U.S. Pat. No. 1,608,689 (issued in 1926), describes an artificial hand comprising fingers and a thumb. The phalanges of each digit are held to their adjacent neighbors using pins.
U.S. Pat. No. 1,742,269 (1930) resorts to the same solution for providing a pivot point between opposing phalanges: pins.
Many more modern joint and prosthetic designs also use pins as the fundamental elements for providing motion between adjacent phalanges. Examples include: U.S. Pat. No. 5,326,369; U.S. Patent Application Publication No. 2004/0054424; U.S. Pat. App. Pub. No. 2006/0212129; U.S. Pat. No. 7,361,197; U.S. Pat. No. 7,655,051; U.S. Pat. App. Pub. No 2012/0203358.
Some different approaches do exist. An example from the WWII era is U.S. Pat. No. 2,500,614 which issued in 1948. This patent discloses a “ball and socket” system for the joints in an artificial hand. However, this solution poses significant manufacturing difficulties and is decidedly more complex in operation than simple pins.
Another prosthetic joint from this era is U.S. Pat. No. 2,549,074 which issued in 1951. Instead of pins, this patent discloses a joint comprising a flat metal sheet. This sheet connects the adjacent ends of the two phalanges. A space between the two phalanges allows the finger to flex into a closed position. Although different in concept than the more prominently used pin, this sheet metal joint still poses some of the same problems as the pin; it holds the adjacent phalanges rigidly fixed in all planes except that plane defined by flexion and extension.
Other prosthetic joints posing the same problems as highlighted above include U.S. Pat. No. 4,193,139, which discloses a pin-joint concept (1980) and U.S. Pat. No. 4,944,758, which discloses a ball-and-socket concept (1990).
All of these solutions tend to either limit motion to one plane, unlike natural joints, which allow some degree of motion in all three dimensions, including rotational movement around the digit's axis, or they require potentially more complicated and costly means for manufacturing and maintenance. It is the aim of this disclosure to overcome these problems, with a design that is simple, compact, waterproof, inexpensive, and easy to maintain.